Found this on RCCL site. Soda is not on the prohibited list here.
https://www.royalcaribbean.com/faq/questions/prohibited-items-onboard-policy
Soda is listed as not allowed here
http://www.royalcaribbean.com/beforeyouboard/whatToKnow/topTenFAQs/detail.do?pagename=top_10_faqs&snav=2&faqId=260
Its confusing. Think I'll printout the first one and take it with, just in case.